The present invention relates to an optical rotary encoder and, more particularly, to an alignment of photosensor elements and a construction of a circuit connected to the photosensor elements.
An optical rotary encoder generally includes a light source, photosensor elements, and a slit plate disposed between the light source and the photosensor elements. A stationary mask plate is interposed between the photosensor elements and the rotatable slit plate so as to control the optical phase of the beam applied to the photosensor elements through the rotating slit plate and the stationary mask plate. Four photosensor elements are generally required so that each photosensor element develops a signal A of a certain phase, a signal A of the inverse phase, a signal B which has a phase difference of 90.degree. with respect to the signal A, and another signal B of the inverse phase to the signal B.
If the four photosensor elements are radially aligned, the encoder system becomes large. If the four photosensor elements are aligned along the circular periphery of the slit plate, the adjustment between the mask plate and the photosensor elements becomes complicated. In both cases, the single substrate carrying the four photosensor elements is considerably long and, therefore, the manufacture thereof is not easy.
Accordingly, an object of the present invention is to provide an optical rotary encoder which includes photosensor elements aligned in a desired form which ensures a stable operation of the optical rotary encoder.
Another object of the present invention is to provide a control circuit which receives output signals of the photosensor elements and stably develops a detection output.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, four photosensors are aligned in a square fashion. A stationary mask is disposed in a manner that two photosensors disposed at the diagonal position confront the slits of inverse phase relationship. The output signals developed from the two photosensors disposed at the diagonal position are applied to a comparator in order to obtain a digitized bipolar detection output signal.